The present invention relates to a heat developing method for heat developable image recording material and, more particularly, to a heat developing method for heat developable image recording material for photomechanical processes. More specifically, the present invention relates to a heat developing method for heat developable image recording material for scanners or image setters.
As one of the light exposure methods of photographic photosensitive materials, there has been known an image forming method of so-called scanner type, in which an original image is scanned and which a silver halide photographic material is light-exposed based on the obtained image signals to form a negative or positive image corresponding to the image on the original image.
As for a case where an image output from a scanner on a film is further printed directly on a printing plate without any reversal step, or a scanner light source having a soft beam profile, a light-sensitive material for scanners exhibiting ultra-high contrast property has been desired.
A large number of photosensitive materials having a photosensitive layer on a support for forming images upon imagewise exposure have been known. Among them, as a system for rendering preservation of environments and image forming means simplified, a technology for forming images by heat development is exemplified.
In recent years, reduction of the amount of waste processing solutions is strongly demanded in the field of photomechanical processes from the standpoint of environmental protection and space savings. To cope with this, techniques are needed in relation to photosensitive heat developable materials for use in photomechanical processes, which can be effectively exposed by a laser scanner or laser image setter and can form clear black images having high resolution and sharpness. Such heat developable photosensitive materials can provide to customers a heat development processing system, without use of solution-type processing chemicals, simpler and free from incurring environmental destruction.
Methods for forming an image by heat development are described, for example, in specifications of U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Klosterboer, Imaging Processes and Materials, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d, 8th ed., page 2, compiled by J. Sturge, V. Walworth and A. Shepp, Neblette (1969). The photosensitive material used contains a light-insensitive silver source (e.g., organic silver salt) capable of reduction, a photocatalyst (e.g., silver halide) in a catalytic activity amount, and a reducing agent for silver, which are usually dispersed in an organic binder matrix. This photosensitive material is stable at room temperature. However, when it is heated at a high temperature (e.g., 80xc2x0 C. or higher) after the exposure, silver is produced through an oxidation-reduction reaction between the silver source (which functions as an oxidizing agent) capable of reduction and the reducing agent. The oxidation-reduction reaction is accelerated by the catalytic action of a latent image generated upon exposure. The silver produced by the reaction of the silver salt capable of reduction in the exposure region provides a black image and this presents a contrast to the non-exposure region. Thus, an image is formed.
Such heat developable photosensitive materials of this type have been known previously, but in most of those photosensitive materials, the photosensitive layer is formed by coating a coating liquid having a solvent of an organic solvent such as toluene, methyl ethyl ketone (MEK), methanol, and the like. Use of such. organic solvents as a solvent not only adversely affects human bodies during manufacturing processes but also is disadvantageous in term of costs due to recycling the solvents and others.
To cope with this, a method has been considered in which a photosensitive layer (hereinafter referred also to as xe2x80x9caqueous photosensitive layerxe2x80x9d) is formed using a coating liquid of a water solvent not having the above problem. For example, Japanese Unexamined Patent Publication [KOKAI] (hereinafter referred simply to as xe2x80x9cJP-Axe2x80x9d) Showa Nos. 49-52,626 and 53-116,144, and the like set forth an example that gelatin is used as a binder. Also, JP-A-50-151,138 sets forth an example that a poly vinyl alcohol is used as a binder.
In JP-A-60-61747, an example that a gelatin and a polyvinyl alcohol are used together is described. In WO97/04,355, an example that a water soluble or water dispersion binder is used in the image forming layer and a water soluble binder such as gelatin, polyvinyl alcohol, cellulose derivatives, or the like is used in a protection layer is described. In addition, as another example other than the above examples, JP-A-58-28,737 sets forth an example of a photosensitive layer that a water-soluble polyvinyl acetal is used as a binder.
Such a binder surely allows to form the photosensitive layer in use of a coating liquid with a water solvent, thereby making such use advantageous in terms of environments and costs.
However, if the polymer such as gelatin, polyvinyl alcohol, water-soluble polyvinyl acetal, and so on is used as the binder, contractions due to dehydration as well as thermal expansions of the binder may occur at the same time and, because different from behavior of the support during thermal expansion, may cause the films to have wrinkles, thereby producing only unsuitable films for color printing in which the film is used in an overlapping manner.
In a meantime, apparatuses and methods for heat developing the heat developable recording material have been generally known, and for example, those are described in U.S. Pat. Nos. 3,629,549, 3,648,019, 3,709,472, and 4,518,845.
Svendsen""s U.S. Pat. Nos. 3,629,549 and 4,518,845, both, disclose developing apparatuses having a drum coaxially attached in and thermally isolated from a heating member.
The sheet made of a film to be developed is engaged with the drum and is driven around the heating member. However, the heat developing apparatus of this type is not suitable for a film having relatively soft thermoplastic polymer binder in the outmost layer. That is, because the surface on a side supporting emulsion comes in contact with the isolation drum and the heating member, the outmost layer of the film may suffer from scratching scars or adhesive marks.
In another type of the heat developing apparatus, a heating drum is incorporated to be statically charged for holding a film during development. With such an apparatus, the outmost layer of the film on a side supporting the emulsion does not contact any structural member, and therefore, no scratching scar described above is made on the surface. However, the electrostatic apparatus used for holding the film on the drum during thermal development is relatively complicated and has a shape not suitable for heat developing a large size film.
Therefore, a technique has been desired to provide a heat developable photosensitive material having good resistance against scratching in use of the aqueous photosensitive layer having advantages in terms of environments and costs, which can be coated with good coating surface quality and may not suffer from beko and side ripples, and a heat developing method thereof.
It is an object of the invention to provide a heat developing method for heat developable image recording material for photomechanical processes, particularly, for scanners or image setters. More specifically, it is an object of the invention to provide a heat developing method for heat developable image recording material with good stability in size before and after heat development in preventing the surfaces of the heat developable image recording material from receiving scars of scratching and adhering during heat development. More particularly, it is yet another object of the invention to provide a heat developable image recording material and a heat developing method in which images can be obtained without processing unevenness but with stable heat developing processing property which provides good conveyance and prevents the surfaces from receiving scratching scars.
The above objects are accomplished by means described below.
This invention is a heat developing method conveying, to make a heating processing on a heater surface, a heat developable image recording material in which an image forming layer and a protection layer are formed using a polymer latex as a binder on one side of a support prepared by subjecting a polyester biaxially drawn and crystallized with orientation to a thermal relaxation processing at a temperature equal to or higher than 130xc2x0 C. and equal to or lower than 200xc2x0 C. at a conveyance tension of 7 kg/cm2 or lower and in which a back layer is formed using a polymer latex as a binder on the other side of the support, the method comprising the steps of: preparing at least two heaters for providing heating processing at a prescribed temperature to the heat developable image recording material disposed securely in line in a conveyance direction of the heat developable image recording material; conveying the heat developable image recording material with a conveying means by sliding the heat developable image recording material on surfaces of the heaters; and thermally processing the heat developable image recording material by pressing at least a part of the heat developable image recording material during conveyance with a pressing means against the surfaces of the heaters.
As suitable embodiments of the heat developing method of the invention, exemplified are: the pressing means is a plurality of pressing rollers disposed on the surface of the heater; the pressing roller is coupled to a rotary driving means and serves as the conveying means for sliding the heat developable image recording material on the surface of the heater; the pressing rollers rotate at the same predetermined circumferential velocity; the respective heaters are plate shaped heaters and arranged in a plane; the respective heaters have a fluororesin coated contact surface in contact with the heat developable image recording material or have a processing sheet made of a fluororesin and disposed at the heaters; a heat developing method processing, with a heating developing apparatus having a preliminary heating section and a heat developing processing section, a heat developable image recording material having on a support at least one image forming layer and at least one protection layer formed on the image forming layer, the method comprising, to make a developing processing, the steps of conveying the heat developable image recording material by opposing rollers in the preliminary heating section, contacting a surface on a side having the image forming layer to a drive roller in the heat developing processing section, and conveying the heat developable image recording material by sliding the back surface located oppositely to the side having the image forming layer in contact with a smooth surface, wherein a linear velocity (line speed) rate of the preliminary heating section to the heat developing section is equal to or lower than 99.9% and equal to or higher than 95.0%; the developing processing is made with the linear velocity of 10 to 40 mm/sec; the heat developing apparatus has a rubber roller, in contact with .he surface on the side having the image forming layer, at least whose surface is made of a rubber having rubber hardness of 50 degrees or below; the roller at least has a surface made of a silicone rubber; the smooth surface of the heat developing processing section of the heat developing apparatus in contact with the back surface located oppositely to the side having the image forming layer is formed of a non-woven fabric made of aromatic polyamide or polytetrafluoroethylene (Teflon); and a clearance between the smooth surface in contact with the surface located oppositely to the side having the image forming layer during conveyance of the heat developable image recording material and the surface of the drive roller in contact with the surface located on the side having the image forming layer during conveyance of the heat developable image recording material is of 0 to 2 mm.
This invention is also to provide a heat developable image recording material processed by the above heat developing method having, at a temperature when heat development is processed, a ratio of a friction coefficient between the surface on the side having the image forming layer and the roller surface of the heat developing processing section to a friction coefficient between the back surface located oppositely to the side having the image forming layer and the smooth surface of the heat developing processing section is set to 1.5 or higher.
As suitable embodiments of the heat developable image recording material of the invention, exemplified are: the friction coefficient between the back surface located oppositely to the side having the image forming layer and the smooth surface of the heat developing processing section is of 1.0 or lower at a temperature when heat development is processed; a polymer latex is used for binders in the image forming layer and the protection layer; at least one conductive layer having a surface specific resistance of 1xc3x971012 xcexa9 or lower under a condition of 25xc2x0 C., 20% RH on the side oppositely to the image forming layer; and a back layer on the side opposite to the side having the image forming layer, wherein a polymer latex is used for binder in the back layer.